Ceramic dielectric block resonator devices such as, for example, ceramic dielectric block filters are well known in the electrical arts and at least one such ceramic filter is described in U.S. Pat. No. 5,162,760 entitled “Dielectric Block Filter with Isolated Input/Output Contacts”. These blocks are relatively easy to manufacture, rugged, and relatively compact. In the basic ceramic block filter design as shown in U.S. Pat. No. 5,162,760, resonators are formed by cylindrical passages called through-holes which extend between opposed top and bottom surfaces of the block. The block is substantially plated with a conductive material (i.e., metallized) on all but one of its six (outer) sides and on the interior walls of the resonator through-holes.
The top surface is not fully metallized but instead bears a metallization pattern designed to couple input and output signals through the series of resonators. In the design of, for example, U.S. Pat. No. 5,162,760 and U.S. Pat. No. 5,745,018 to Vangala, the pattern extends to the sides of the block, where input/output electrodes or contacts are formed.
The reactive coupling between adjacent resonators and thus the performance of the device is dictated, at least in part, by the physical dimensions and number of resonators, by the orientation of the resonators relative to one another and the PC board to which the filter is adapted to be mounted, and by aspects of the top surface metallization pattern. These filters may also be equipped with an external metallic shield of the type disclosed in, for example, U.S. Pat. No. 5,745,018 to Vangala which is attached to and positioned across the open-circuited end of the block in order to minimize parasitic coupling between non-adjacent resonators and achieve acceptable stopbands.
Although such RF signal filters have received widespread commercial acceptance, efforts at improving this basic design and, more specifically, efforts at improving the frequency response of such filters outside their bandwidth, i.e., improved attenuation in the stopband, have continued to the present.
For example, in U.S. Pat. Nos. 5,162,760 and 5,745,018, the input/output contacts/pads are located on one of the side surfaces adjacent the top surface to allow the filter to be direct surface mounted on a printed circuit board in a relationship where the resonator through-holes are oriented parallel to the face of the printed circuit board to which the filter is adapted to be mounted. A disadvantage associated with this design, however, is the fact that it has a limited effect of attenuation in the stop band of the filter, mostly due to its asymmetrical excitation.
As another example, U.S. Pat. No. 5,130,682 discloses a filter where a special mounting bracket is used for suppressing unwanted signals. The bracket, however, does not allow for the tuning of the filter inasmuch as the pattern on the top surface of the filter is not accessible through the bracket.
The present invention is directed to an improved resonator/filter device as described in more detail below.